Astronomical Observatory: Cool Images

M43, Matthias Landheer

M43, or
De Mairan's Nebula, is actually a part of M42, the Great Orion Nebula. M43 and M42 are separated by a lane of black space. This black lane is dust that is in front of both nebulas. M43 is a diffuse nebula. Diffuse nebulas are thin, spread-out clouds of gas, mostly hydrogen, and dust. M43 is an emission and a reflection diffuse nebula. Emission means that the stars near it give off enough heat and ultraviolet radiation to excite the hydrogen gas of the nebula which gives it the reddish tinge on the top half. Reflection means that the dust is behind the star and the light shines on the star and is reflected back to us as the bluish tinge on the bottom half. This gives the nebula its variety of colors. M43 is about 1,500 light years away. It was discovered in 1731 by
Jean-Jacques Dortous de Mairan who described it as a "brilliance surrounding a star...very similar to the atmosphere of our Sun."

In the image we can see the colors red, blue, and a bit of green surrounding the white core. These are the colors that are formed from the excitement and reflection of the nearby stars. We can see a few stars close around the image and there is a core star in the middle as well. This core star is the one that emits the radiation necessary to make the top half of the nebula red and also shines on the dust to make the bottom half blue. The angular size of M43 is 3.5 arc minutes. The linear size of M43 is 1.55 light years.